They can point to the 1947 Partition Plan which explicitely stated that sovereignty over this territory would came their way the moment that the Mandatory packed its bags and went home. What they lack is "authority", precisely because their sovereign territory has continuously been under one (Jordanian) or other (Israeli) belligerent occupation since the Mandatory packed its bags and went home. Occupation does not extinguish Sovereignty, Cipora, precisely because an "occupation" isn't a "conquest".
UN aid chief says no warring parties observed Yemen truce (Reuters)
from the article: Israel can't stop Palestinian independence